Reject loop candidates that contain catch blocks

[a7ehuo]

Reject natural loops as idiom candidates if any catch handler block appears in the loop region (including nested blocks). Loops containing catch blocks are not suitable for CISC idiom transformations (e.g., MemSet/MemCpy) because the exception path alters the loop region’s CFG and prevents extraction/alignment of the required idiom region. This change avoids wasted idiom analysis on loops whose CFG contains exception-handler paths.

Related: #21417

[a7ehuo]

@hzongaro May I ask you to review this change? Thank you!

@jdmpapin fyi

[a7ehuo]

Here are some more details on how createLoopCandidates treats different types of loops without and with this change.

Loop Types	Baseline	With this change
Loop Type 1	accept	reject
Loop Type 2	Inner loop is accepted. Outer loop is rejected because it doesn't have block structure.	Inner loop is rejected. Outer loop is rejected because it doesn't have block structure.
Loop Type 3	Inner loop is accepted.  Outer loop is rejected because it is not inner most loop.	Inner loop is accepted.  Outer loop is rejected because it is not inner most loop.
Loop Type 4	Inner loop is accepted.  Outer loop is rejected because it is not inner most loop.	Inner loop is rejected.  Outer loop is rejected because it is not inner most loop.

Loop Type 1

        for (int i = 0; i < a.length; i++) {
            try {
                a[i] = v;
            } catch (ArrayIndexOutOfBoundsException e) {
                // swallow (intended unreachable)
                sink++;
            }
        }

Loop Type 2

       for (int r = 0; r < aa.length; r++) {
            byte[] a = aa[r];
            for (int i = 0; i < a.length; i++) {
                try {
                    a[i] = v;
                } catch (ArrayIndexOutOfBoundsException e) {
                    sink++;
                }
            }
        }

Loop Type 3

       for (int r = 0; r < aa.length; r++) {
            byte[] a = aa[r];
            try {
                for (int i = 0; i < a.length; i++) {
                    a[i] = v;
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                sink++;
            }
        }

Loop Type 4

       for (int r = 0; r < aa.length; r++) {
            byte[] a = aa[r];
            try {
                for (int i = 0; i < a.length; i++) {
                    try {
                        a[i] = v;
                    } catch (ArrayIndexOutOfBoundsException e) {
                        sink++;
                    }
                }
            } catch (ArrayIndexOutOfBoundsException e) {
                sink++;
            }
        }